On the Nature of the Heat Stabilizing Effect of Inorganic Ions on Escherichia coli

The growth lag of Escherichia coli at 45°C was reduced by the addition of sodium, potassium, magnesium and calcium ions to the growth medium. A method to quantitatively determine the lag-reducing effect of these ions was developed. The results obtained showed that equivalent amounts of the ions produced the same reduction of the growth lag. According to the results of plasmolysis experiments cells of E. coli suspended in peptone broth were permeable to all four ions. The course of plasmolysis and subsequent deplasmolysis was registered as changes in the cells' ability to scatter light. The heat stability of catalase from E. coli was increased by addition of the four ions. This was observed in experiments with intact cells and with a crude cell-free preparation of catalase. The results of our experiments are most easily explained by assuming a stabilizing effect of the ions tested on the intracellular bacterial proteins.